1. Field of the Invention
The present invention relates generally to electronic devices and circuits and, more particularly, to a solid state optoelectronic switching and display device and a method of its manufacture.
2. The Prior Art
Electronic integrated circuits (IC's) and very-large-scale integrated circuits (VLSI's), both commonly referred to as chips, are formed of silicon (Si). Silicon and the chips made from silicon are the basic building blocks of computer systems. Typically, PC boards contain over 300 chips, and VLSI chips have about 500 to 1,000 wire-bonded pins. The interconnections among the myriad component parts of computer systems are still formed, however, by low speed large area nests of copper wiring, soldered or otherwise secured to pins of chips to convey data electrically therebetween. Such low speed interconnectings create massive bottlenecks in data transfer between chips and PC boards. Further, computer displays of processed data are, for the most part, bulky cathode ray tubes. As a consequence, present day computers are not only heavier and bulkier than they could be, but also are slower than they need be. A monolithically integrated all solid state system could solve both drawbacks. Such an all solid state system will allow not only for fast and efficient information processing within the chips of the system but also for rapid and efficient transfer of data among those chips. Further, such an all solid state system also will allow for considerable reduction in both weight and bulk therein, featuring flat panel optical displays. One suggested solution lies in using solid state devices whose output is electromagnetic radiation rather than electricity. A solid state system employing data transfer in the form of electromagnetic radiation allows serial, rather than parallel, data transfer at near the speed of light and with low power consumption, no RF interference problems, and with high reliability.
Most workers in the field have concentrated their efforts in providing hybrid approaches by employing standard GaAs light-emitting devices in an otherwise solid state system based on silicon. The most promising III-V light-emitting compounds, however, are not suitable for direct deposition onto silicon substrates due, inter alia, to lattice and thermal expansion coefficients mismatch. Consequently, the performance characteristics of III-V compound light-emitting devices formed on silicon have been unacceptably low. Approaches involving securing GaAs-type devices onto silicon wafer surfaces by soldering or with glue have proved to be a labor intensive, time consuming, hence costly procedure. Although GaAs and its alloys offer the promise of lightweight, polychrome flat panel displays for computers, these compound semiconductors generally are found to be far too expensive for use as large area video display panels for computers. Low cost visible light emitters based solely on solid state silicon technology could be the answer to most, if not all, of the above problems.
Standard crystalline silicon is, however, unsuitable for light emission due to its indirect optical band gap. Certain III-V compounds, in contrast, possess a direct energy gap corresponding to wavelengths in the red, the orange, the yellow, and the green regions of the visible spectrum. Although some luminescence in the near infrared (near IR) region in standard crystalline silicon samples is detectable, such luminescence is extremely weak and of no practical use for light emission devices.
Some workers in the field have recently observed that porous silicon, a spongy phase of Si, also referred to as mesoporous Si, exhibits quantum confinement effects leading to a considerable increase in the effective energy gap. See V. Lehmann et al., "Porous Silicon Formation: A Quantum Wire Effect," App. Phys. Lett. 58 (8), 25 Feb. 1991, pgs. 856-858. Another worker in the field has reported observing visible red photoluminescence from porous silicon when excited by an argon laser. See L. T. Canham, "Silicon Quantum Wire Among Fabrication by Electrochemical and Chemical Dissolution of Wafers," Appl. Phys. Litt. 57 (10), 3 Sep. 1990, pgs. 1046-1048. Recently, other workers have succeeded in forming liquid junction devices using aqueous HCl or KNO.sub.3 solutions to contact porous silicon. The red light emission of their devices, however, lasted only a few minutes due to oxidation reactions at the porous Si/aqueous interface. See A. Halimaoui et al., "Electroluminescence In The Visible Range During Anodic Oxidation of Porous Silicon Films," App. Phys. Lett 59 (3), 15 Jul 1991, pgs. 304-306. That an impenetrable film of silicon oxide will form on a silicon surface subjected to an anodic bias in an aqueous environment is well established from thermodynamic principles.